I will be getting my ACF into a new 20 gallon long aquarium, and am looking for good filters. I'm used to heavy turtle filtering, but I'm not so sure about aquatic frog filtering parameters with regards to GPH or tank ratings (i.e., should I be using a filter rated for 40 gallons with a 20 long, or can I use a 20 gallon-rated filter with the 20 gallon tank since the frog is the sole occupant, and there are no plants, fish, substrate, etc.?). Also, any suggestions on filter styles are welcome--is a strong HOB filter going to work, or do I need something like a Tetra Whisper? (Although they are very similar in the first place).

Thanks!